Baud-rate timing recovery

Abstract

A system and a method for simple and robust baud-rate timing recovery suitable for jointly operating with a decision-feedback equalizer are disclosed. Timing functions for timing recovery are extracted only from filter coefficients of feed-forward and feedback filters. The relation between the coefficients of feed-forward filter and the impulse response is derived under a zero-forcing condition while the relation between the coefficients of the feedback filter and the impulse response is known. Based on the relations, several timing functions with varied degrees of computation are derived, which can drive the sampling instances approximately at the peak point of the channel impulse response. Since the derived timing functions use equalizer coefficients, they work jointly with equalization even without using a training sequence. Simulation results over 5-m and 100-m UTP Category-5 cables at 125M Baud show fast and robust timing recovery operation in a phase-locked loop.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application relates to U.S. patent application Ser. No. 60 / 176,416, entitled “Baud-Rate Timing Recovery,” filed on Jan. 14, 2000, which is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to data communication systems and methods. More particularly, this invention relates to a system and method for timing recovery.[0004]2. Description of the Background Art[0005]Communication systems increasingly depend on digital data transmission. Digital data transmission, in turn, depends on reliable reception of transmitted data. Effective timing recovery facilitates reliable reception of transmitted data in a digital data receiver. More specifically, effective timing recovery facilitates correct sampling instances of the received data stream. In other words, certain digital data receivers continuously adjust the frequency and phase of the receiver clock to op...

AI Technical Summary

Benefits of technology

[0015]The present invention provides baud-rate timing recovery methods and systems for recovering timing information from a transmitted signal. Versions of the invention combine timing recovery with equalization. One embodiment achieves the equalization using a decision feedback equalizer (DFE). A DFE enjoys wide popularity in digital data receivers because of its superior

Problems solved by technology

For example, with respect to the first method described above, a receiver performing baud sampling does not detect signal crossings with any useful precision.

Unfortunately, the use of higher sampling rates or additional sampling of the signal derivative for timing recovery is not an appealing solution because of the corresponding increase in expense, complexity, and amount of hardware.

Hence, when using a channel that severely distorts the transmitted signal, the Muller and Muller scheme can fail to operate properly without a training sequence.

However, if the system does not incorporate a training sequence, the automatic equalizer will not accurately estimate the incoming data values until the equalizer settles.

Furthermore, when the timing of the sampling instants drifts the equalizer typically does not achieve stable operation.

However, this method inherits the traditional problems present in a linear equalizer, such as noise enhancement.

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